Rhamnose is a deoxy sugar found in plants and some bacteria, used as a structural component of plant cell walls and in polysaccharides. It is also used in the pharmaceutical, agricultural, and cosmetic industries, and as a commercial source of rhamnolipids. Rhamnolipids have surfactant properties and are considered a green alternative to petroleum-based products. They are also used as a trigger for gene production in genetically modified bacteria and in a test for intestinal permeability in humans.
Rhamnose is an unusual sugar found mostly in plants and some bacteria. Unlike most naturally occurring sugars, it is found in an L configuration instead of the usual D configuration. It forms an important structural component of plant cell walls and is also bound to other compounds, such as phenols. In some gram negative bacteria, sugar is bound to lipids. Both the pure compound and the lipid component have numerous uses in the pharmaceutical, agricultural and cosmetic industries.
In addition to its unusual L-shaped structural configuration, this unusual compound is also atypical because it is a deoxy sugar. Such sugars are usually components of DNA or RNA. This compound is found as a simple sugar in some plants, but is more commonly found as a glycoside. Such structures combine a sugar with another compound, such as a phenolic.
A very important and widespread use of this sugar in plants is as a component of polysaccharides known as rhamnogalacturonans. These polymers are important for the structural integrity of plant cell walls and include part of pectin, one of the substances that holds plant cell walls together. These are long chains of L-rhamnose mixed with galacturonic acid. There are several types of rhamnogalacturonans that vary in their degree of branching and components, which may include other sugars.
Bacteria known as mycobacteria have rhamnose in their outer membrane. Such bacteria include the random agent of tuberculosis. Drugs targeting the synthesis of this sugar are being studied as possible clinical agents to treat this disease.
Other bacteria use rhamnose combined with lipids in their polysaccharides, resulting in compounds called rhamnolipids. Those produced by the gram-negative bacterium Pseudomonas aeruginosa are used commercially. At least one other type of gram-negative bacterium has been genetically engineered to produce a higher percentage of rhamnolipid in the exopolysaccharide surrounding cells to facilitate better extraction of the compound for industrial uses.
Rhamnolipids have surfactant properties, which means they can mix with oil and water. Most of these compounds were produced from petroleum products in the past. These naturally based compounds are considered a green alternative to older products and are often used in cosmetics, pharmaceuticals and agriculture.
In addition to the direct use of rhamnolipids, they are also used as commercial sources of rhamnose sugar. It is not ideal to have plants as a source of an industrial compound, as their availability may be limited. Many companies prefer to obtain industrial natural products from genetically modified sources.
There are a host of other uses for this sugar. For example, there is an overexpression system in which the production of the desired gene is triggered by adding sterilized rhamnose to the genetically modified bacteria. A rhamnose test for intestinal permeability in humans is available. Many prescription drugs, such as nonsteroidal anti-inflammatory drugs (NSAIDs), can cause intestinal damage that manifests as leakage through the intestines. Having patients drink a solution of lactulose and L-rhamnose is one way to test for this condition.
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